I've seen strong evidence that Amazon suppresses negative reviews if the product seller wants them suppressed. Most don't ask for censorship, so there are still a lot of hostile reviews, but I don't consider Amazon reviews a trustworthy measure.
It's also possible for a competitor or someone with a grudge to flood sites with libelous reviews under different names and IP addresses, so you can't tell much from that either. I don't worry until I see something from identifiable, somewhat trustworthy sources.
I poked around, and found some evidence that amazon sporadically censors negative reviews, though I haven't seen the strong evidence.
Consumeraffairs.com has a very neutral wikipedia page-- nothing about whether it's apt to be used for completely false campaigns.
I checked the Better Business Bureau about Purina, and they just had a few complaints listed-- only two of them had details, and neither of them were about extremely bad pet food.
Metafilter had something about the salmonella recall, but nothing about serious current problems. Neither did Snopes.
I've googled on [purina maggots] and [kit and kaboodle complaints +purina] and turned up very little.
I find it bizarre that there might be an energetic anti-purina campaign which is limited to consumeraffairs.com, but that seems like the best explanation so far.
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